/* * Copyright (C) 2007 The Guava Authors * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.google.common.collect; import com.google.common.annotations.GwtCompatible; import java.util.Collection; import java.util.Map; import java.util.Set; import javax.annotation.Nullable; /** * A collection similar to a {@code Map}, but which may associate multiple * values with a single key. If you call {@link #put} twice, with the same key * but different values, the multimap contains mappings from the key to both * values. * *
The methods {@link #get}, {@link #keySet}, {@link #keys}, {@link #values}, * {@link #entries}, and {@link #asMap} return collections that are views of the * multimap. If the multimap is modifiable, updating it can change the contents * of those collections, and updating the collections will change the multimap. * In contrast, {@link #replaceValues} and {@link #removeAll} return collections * that are independent of subsequent multimap changes. * *
Depending on the implementation, a multimap may or may not allow duplicate * key-value pairs. In other words, the multimap contents after adding the same * key and value twice varies between implementations. In multimaps allowing * duplicates, the multimap will contain two mappings, and {@code get} will * return a collection that includes the value twice. In multimaps not * supporting duplicates, the multimap will contain a single mapping from the * key to the value, and {@code get} will return a collection that includes the * value once. * *
All methods that alter the multimap are optional, and the views returned
* by the multimap may or may not be modifiable. When modification isn't
* supported, those methods will throw an {@link UnsupportedOperationException}.
*
* @author Jared Levy
* @param Some multimap implementations allow duplicate key-value pairs, in which
* case {@code put} always adds a new key-value pair and increases the
* multimap size by 1. Other implementations prohibit duplicates, and storing
* a key-value pair that's already in the multimap has no effect.
*
* @param key key to store in the multimap
* @param value value to store in the multimap
* @return {@code true} if the method increased the size of the multimap, or
* {@code false} if the multimap already contained the key-value pair and
* doesn't allow duplicates
*/
boolean put(@Nullable K key, @Nullable V value);
/**
* Removes a key-value pair from the multimap.
*
* @param key key of entry to remove from the multimap
* @param value value of entry to remove the multimap
* @return {@code true} if the multimap changed
*/
boolean remove(@Nullable Object key, @Nullable Object value);
// Bulk Operations
/**
* Stores a collection of values with the same key.
*
* @param key key to store in the multimap
* @param values values to store in the multimap
* @return {@code true} if the multimap changed
*/
boolean putAll(@Nullable K key, Iterable extends V> values);
/**
* Copies all of another multimap's key-value pairs into this multimap. The
* order in which the mappings are added is determined by
* {@code multimap.entries()}.
*
* @param multimap mappings to store in this multimap
* @return {@code true} if the multimap changed
*/
boolean putAll(Multimap extends K, ? extends V> multimap);
/**
* Stores a collection of values with the same key, replacing any existing
* values for that key.
*
* @param key key to store in the multimap
* @param values values to store in the multimap
* @return the collection of replaced values, or an empty collection if no
* values were previously associated with the key. The collection
* may be modifiable, but updating it will have no effect on the
* multimap.
*/
Collection Changes to the returned collection will update the underlying multimap,
* and vice versa.
*
* @param key key to search for in multimap
* @return the collection of values that the key maps to
*/
Collection When passed a key that is present in the map, {@code
* asMap().get(Object)} has the same behavior as {@link #get}, returning a
* live collection. When passed a key that is not present, however, {@code
* asMap().get(Object)} returns {@code null} instead of an empty collection.
*
* @return a map view from a key to its collection of values
*/
Map In general, two multimaps with identical key-value mappings may or may
* not be equal, depending on the implementation. For example, two
* {@link SetMultimap} instances with the same key-value mappings are equal,
* but equality of two {@link ListMultimap} instances depends on the ordering
* of the values for each key.
*
* A non-empty {@link SetMultimap} cannot be equal to a non-empty
* {@link ListMultimap}, since their {@link #asMap} views contain unequal
* collections as values. However, any two empty multimaps are equal, because
* they both have empty {@link #asMap} views.
*/
@Override
boolean equals(@Nullable Object obj);
/**
* Returns the hash code for this multimap.
*
* The hash code of a multimap is defined as the hash code of the map view,
* as returned by {@link Multimap#asMap}.
*/
@Override
int hashCode();
}